The paraventricular nucleus (PVN) of hypothalamus is emerging as a central site for the integration and coordination of some neuroendocrine and autonomic visceral responses and its importance in the maintenance of homeostasis is proposed. Efferent fiber projections of PV neurons to the pituitary gland and specific brainstem centers associated with the control of cardiovascular and respiratory functions are known. The studies proposed will further our understanding of the organization of afferent peptidergic fiber projections to the paraventricular nucleus and elucidate the significance of these pathways in relation to the neuroendocrine and autonomic functions of the PVN. The specific aims of this proposal are (1) to describe the cytoarchitectonic organization of ACTH/Beta-endorphin, enkephalin and somatostatin immunoreactive neurons within the functionally distinct subnuclei of the PVN complex and (2) to elucidate the intrinsic synaptic organization and potential interactions and communications of these three central peptidergic systems and magnocellular (vasopressin/oxytocin) PV neurons. The studies proposed will provide an anatomical substrate for functional interactions described between each of the selected neuropeptidergic systems and magnocellular neurons to occur. These findings will be of considerable importance to the neuroendocrinologist interested in the control mechanism of vasopressin and oxytocin secretion and their effects on neuroendocrine and autonomic visceral (e.g. cardiovascular) functions. Anatomical details will be elucidated using Vibratome tissue sections and the basic and double antigen immunocytochemical procedures at both the light and electron microscopic levels.